Iraqi forces advanced Monday after launching "the mother of all battles" aimed at retaking Mosul and dealing a death blow to Isil's "caliphate" in the city where it was declared two years ago.

The start of the long-awaited assault raised deep concerns for hundreds of thousands of civilians trapped in Iraq's second-largest city, with aid groups warning of a massive humanitarian crisis.

Some 30,000 federal forces are leading the offensive, backed by air and ground support from a 60-nation US-led coalition, in what is expected to be a long and difficult assault on Isil's last major Iraqi stronghold.

Iraqi forces could be seen readying weapons and ammunition as columns of armoured vehicles headed towards Mosul from the town of Al-Shura, some 30 miles south of the city.

Watch | Battle to recapture IS-held Mosul begins

01:20

The Pentagon described the operation as a "decisive moment" in the fight against Isil but the US-led coalition's top commander warned it could last weeks or more.

Iraqi Prime Minister Haider al-Abadi announced the beginning of the assault in a televised address in the early hours of Monday.

"Today I declare the start of these victorious operations to free you from the violence and terrorism of Daesh (Isil)," Abadi said.

Isil seized control of large parts of Iraq and neighbouring Syria in mid-2014, declaring a cross-border "caliphate" and committing widespread atrocities.

The jihadists have suffered a string of territorial defeats this year in both countries, and the retaking of Mosul would all but end the group's presence in Iraq as a land-holding force.

Iraqi forces have been closing in on Mosul in recent weeks but the battle launched on Monday could be the toughest yet in the fight against Isil.

The terror group's forces are vastly outnumbered, with an estimated 8,000 jihadists in the city and surrounding area.

But they have had months to prepare and will seek to use hit-and-run tactics, ambushes, snipers, bombs, berms and trenches to slow down and bleed Iraqi forces.

Watch | US-led airstrike destroys Isil ‘car bomb factory’ near Mosul

00:26

In a statement released online after the beginning of the assault, Isil claimed it launched a series of deadly suicide car bomb attacks against Iraqi forces.

As the assault began, federal forces moved from their main staging base of Qayyarah, south of Mosul, while Peshmerga forces from the autonomous Kurdish region advanced from the east.

Around 4,000 Kurdish Peshmerga took part in a push to reclaim villages once inhabited by members of the Christian and Kakai minorities, a statement said.

Smoke rises from what was thought to be an Isil car bombCredit:
Sam Tarling/Telegraph

Several villages were promptly recaptured and Peshmerga forces had moved to the edges of Qaraqosh and Bartalla, two Christian towns seized by IS in August 2014, commanders said.

At a staging area near the village of Khazir east of Mosul, Kurdish forces could be seen firing artillery and rockets as smoke rose from houses in the distance.

The United Nations and other aid organisations warned that a huge number of civilians were in immediate danger.

"I am extremely concerned for the safety of up to 1.5 million people," the UN deputy secretary general for humanitarian affairs and emergency relief, Stephen O'Brien, said.

The UN's humanitarian coordinator in Iraq, Lise Grande, told reporters that an exodus could begin within a week.

Kurdish Peshmerga engineers look for mines near the the village of ShakoliCredit:
Sam Tarling/Telegraph

"It's a trickle right now," she said.

But "our expectation, based on what the military has briefed us (on), is that if we start to see significant population movements, it's likely to be within five to six days."

Iraqi forces advancing on multiple fronts are some distance from Mosul and are expected to eventually take up positions on the edge of the city and lay siege before breaching its boundaries and directly engaging die-hard jihadists.

"This operation to regain control of Iraq's second-largest city will likely continue for weeks, possibly longer," warned Lieutenant General Stephen Townsend, commander of the US-led coalition.

Most of the coalition's support has come in the shape of air strikes and training but US, French and British special forces are also on the ground to advise local forces in battle.

President Recep Tayyip Erdogan on Monday indicated that Turkey would also play a role in the offensive despite concerns raised by Baghdad over Ankara's involvement.

"We will be in the operation and we will be at the table," Erdogan said in a televised speech. "It is out of the question that we are not involved."

As the biggest Iraqi military operation since the 2011 withdrawal of US troops unfolded, a Turkish delegation arrived in Baghdad for talks and coalition defence ministers agreed to meet in Paris on October 25 to take stock.

Isil once controlled more than a third of Iraq's territory but its self-proclaimed "state" has been shrinking steadily.

Smoke rises from clashes in the east of Mosul Credit:
Azad Lashkari/Reuters

It lost its emblematic bastion Fallujah in June, the Anbar provincial capital Ramadi months earlier and on Sunday Syrian rebels retook the town of Dabiq, which held special ideological significance for the group.

If Mosul falls to Iraqi forces, only Raqa in Syria would remain as the last major city in either country under Isil control.

But even the recapture of Mosul will not mark the end of the war against Isil, which is likely to increasingly turn to insurgent tactics as it loses more ground.

Just hours after the offensive was launched, Isil claimed responsibility for a suicide car bombing targeting an Iraqi army checkpoint south of Baghdad that killed at least 10 people.

The jihadists have claimed a string of deadly bomb attacks in Baghdad in recent days.

- Report by AFP

Follow the latest updates below from@josiensor, the Telegraph's Middle East correspondent, who is in Khazir, Iraq: ​

Isil could retaliate with 'wave of suicide bombings'

Isil could retaliate with a wave of suicide bombings across Iraq as they are driven out of Mosul, according to Prof Gareth Stansfield, Professor of Middle East Politics at the University of Exeter.

He said: “IS will remain dangerous and pose a threat to the security of all of Iraq’s cities in the months ahead, as the surviving forces return to the asymmetric techniques that have been sharply honed in Iraq and Syria for many years.

"Iraqi security officials fear a wave of bomb attacks , suicide attacks, and car bomb attacks in the period following Mosul’s retaking.”

He warned Western air power would be of limited use once fighting reached built up areas of the city.

"Time and time again, Western air power has been called in to remove difficult and dangerous pockets of IS resistance.

"But this tactic runs into a problem in the heavily populated urban environs of Mosul.

"As the Iraqi Security Forces and Kurdish Peshmerga enter Mosul, they may well find the advance slows to the pace of taking each and every building, room by room.”

Peshmerga 'will retake nine villages by the weekend'

Isil 'will be asking themselves how much they are willing to commit to a losing battle'

Here's what analysts at IHS Country Risk, Zaineb Al-Assam and Columb Strack, have to say about how long the offensive could carry on for:

Most Iraqis anticipate that the operation will be a long and difficult one potentially spanning months.

The Islamic State will be asking themselves how much of their dwindling resources they are willing to commit to a losing battle, at a time when they face an existential threat to the core of their Caliphate in Syria.

Last week, reports emerged of a convoy of IS militants and their families from Mosul arriving in Raqqa.

Back in July 2016, Iraqi news reports claimed 1500 IS members including senior leadership had fled to Syria soon after the recapture of Qayyarah airbase.

However, Islamic State militants can utilise the network of tunnels it has built in preparation for the offensive in order to put up a fierce fight.

Mosul has been the epicentre of the Islamic State’s chemical weapons capability. They have frequently used chlorine and mustard agent against the Kurds and the Iraqi Security Forces around Mosul over the last year, and chemical weapons are likely to play a role in their defence of the city.

The bulk of the Islamic State’s forces in Mosul are locals, many of which have been conscripted against their will.

Order is maintained by a relatively small number of ideologically committed foreign fighters under threat.

The ability of these foreign fighters to maintain order among the ranks and to prevent defections will be a key determinant of how long the battle is likely to take.

As Iraqi forces close in on Mosul, this may embolden local Mosul resistance including the Mosul Brigades who have only been able to mount a very limited- albeit symbolic resistance- to Islamic State prior to the operation.

In the coming weeks/months as the fight enters urban areas, their participation may prove invaluable in providing intelligence on Islamic State whereabouts.

Isil are 'on the back foot', says Fallon

Peshmerga forces gather in the east of Mosul Credit:
Reuters

As the assault began, Michael Fallon, the Defence Secretary, said Isil "are on the back foot".

"The beginning of the encirclement of Mosul today is a big moment in our efforts to rid Iraq of Daesh. Mosul is a large and complex city and operations there will be tough but with Coalition support Iraqi forces will prevail," he said.

RAF jets and drones helped pave the way for Iraqi and Kurdish forces by hitting Isil artillery and fortifications.

Britain has already carried out more than 200 air strikes since the end of June during the Mosul campaign.

In the 72 hours before the attack, RAF Typhoons, Tornados and Reaper drones hit rocket launchers, ammunition stockpiles, artillery pieces and mortar positions and strikes have continued today.

British special forces troops are also taking part in the assault, advising Kurdish troops on the front line and helping call in air strikes.

One Iraqi military source said: "There are British advisers right near the front. They want to get involved."

US-led airstrike destroys Isil ‘car bomb factory’ near Mosul

Isil launches suicide attacks on Kurdish forces

An Isil-run media outlet says the group has launched a series of suicide attacks targeting Kurdish forces advancing on the militant-held city of Mosul.

The Aamaq news agency is claiming eight suicide attacks against the Kurdish fighters, known as Peshmerga, and says Isil destroyed two Humvees belonging to the Kurdish forces and Shiite militias east of the city.

The Kurdish Rudaw TV meanwhile broadcast images of Kurdish tanks firing on two Isil suicide truck bombs, one of which crashed and exploded.

- AP

Kurdish Peshmerga soldiers fire a rocket towards the village of Sharlouki on October 17Credit:
Sam Tarling/Telegraph

Kurdish Peshmerga drive nearr the village of Sheikh Emir, which has been heavily bombardedCredit:
Sam Tarling/Telegraph

Kurdish Peshmerga engineers look for mines near the the village of ShakoliCredit:
Sam Tarling/Telegraph

Smoke rises from what was thought to be an Isil car bomb in the village of ShakoliCredit:
Sam Tarling/Telegraph

Iraqi Army humvees drive near the village of Sheikh EmirCredit:
Sam Tarling/Telegraph

Smoke rises over the village of Sheikh Emir, which has been heavily bombarded by Kurdish PeshmergaCredit:
Sam Tarling/Telegraph

Foreign Office - 'Time to end two years of brutal rule for people of Mosul under Isil'

“The start of Iraqi operations to retake the city of Mosul marks another step forward towards clearing Daesh from Iraq.

"After two years of brutal rule, the people of Mosul can start to have hope for a better future.

“This will be the greatest challenge that Iraq’s Security Forces have yet encountered – they are up to that challenge. The UK, as part of the Global Coalition, is committed to continuing to provide the government of Iraq with military, humanitarian and stabilisation support.”

'This is a decisive moment' - US Secretary of Defence

In Washington, Defence Secretary Ash Carter called the launch of the Mosul operation "a decisive moment in the campaign" to deliver a lasting defeat to IS.

Iraqi forces have been massing around the city in recent days, including elite special forces that are expected to lead the charge into the city, as well as Kurdish forces, Sunni tribal fighters, federal police and Shiite militia forces.

Iraqi Kurdish Peshmerga fighters stand next to a fire as they gather on the top of Mount Zardak, about 25 kilometres east of Mosul, on early October

South of Mosul, Iraqi military units are based at the sprawling Qayara air base, but to the city's east, men are camped out in abandoned homes as the tens of thousands of troops massed around the city have overwhelmed the few military bases in the area.

Kurdish forces are stationed to the north and east of Mosul, a mostly Sunni city that has long been a center of insurgent activity and anti-central government sentiment after the U.S.-led invasion of Iraq in 2003.

In this Friday Oct 14 2016 file photo an Iraqi special forces soldier clutches his rifle ahead of the assault on Mosul

Iraqi officials have warned that the Mosul operation has been rushed before a political agreement has been set for how the city will be governed after IS.

Lt. Col. Amozhgar Taher with Iraq's Kurdish forces, also known as the peshmerga, said his men would only move to retake a cluster of mostly Christian and Shabak villages east of Mosul and would not enter the city itself due to their concern for "sectarian sensitivities." Taher spoke at a makeshift base in an abandoned house along the front line, some 30 kilometers (19 miles) east of Mosul.

British charity prepares to send aid to Mosul

Aid agencies are now in a race against time to get supplies and medical assistance to Mosul.

Among them is the British charity Shelterbox, which builds basic housing facilities for those displaced by conflict or natural disasters.

Iraqi forces deploy in the area of al-Shourah some 45 kms south of MosulCredit:
AFP

Shelterbox's Rachel Harvey, who is based in Erbil, said: "The aim is to get aid to displaced families as quickly as possible. So we are prepositioning stock close to places where we think they might arrive.

"They are likely to be exhausted and traumatised by their recent experiences. Giving people shelter and essential items such as a solar lamp, blankets and a water carrier will allow them a degree of dignity and security to rest and recover.’

More than a million civilians in Mosul facing 'impossible decision'

More than one million people, including hundreds of thousands of children, are facing an "impossible decision" as a huge military assault is launched in Iraq against Islamic State (IS) fighters, reports the Press Association.

Coalition forces are backing local government and Kurdish military with air strikes in an attempt to take Mosul, the country's second largest city, back from IS rule.

Safe escape routes out of the city for civilians caught up in the bloody conflict "do not exist", Save the Children has warned.

Smoke rises from the village of Sharlouki after it was hit by an airstrikeCredit:
Sam Tarling for the Telegraph

Families and children have been advised by local forces to stay inside and erect a white flag on their homes in a bid to stay safe, the charity's spokesman, Ruairidh Villar, said.

Speaking from Irbil, he told the Press Association: "Whether families and children stay or they flee, right now it's an impossible decision."

Save the Children, which said humanitarian agencies are able to get no closer than 30 miles (48km) to the city, is calling on people to urge the Government to do what it can to ensure there are safe pathways for people to leave the area.

Kurdish Peshmerga soldiers fire a rocket towards the village of SharloukiCredit:
Sam Tarling for the Telegraph

He said: "We are calling on the UK Government to put pressure on the Iraqi and coalition forces around Mosul now to establish safe corridors, safe escape routes for children to get out."

Children in Mosul, which has been under IS control for two years, face further trauma amid the bombardment of the city, Mr Villar said.

Kurdish Peshmerga soldiers wait at an artillery position on Zertek mountainCredit:
Sam Tarling

"These children have been through two years of IS rule, subject to an education which is focused on extremist violence," he said, adding that much planning has gone into military operations but not necessarily the humanitarian fallout.

"Some children have not gone to school at all. There's been a lack of food and medicine and after all that they're going to have to escape from what looks to be a very bloody conflict indeed."

The charity said the UN's emergency appeal is not well enough funded, meaning camps only ready to house around 60,000 people could be "overwhelmed within days".

Assault on Mosul gathers pace

3,000 Iraqi soldiers trained by Turkey in bid to drive Isil from Mosul

Around half of some 3,000 Iraqi forces trained by Turkey at the Bashiqa camp in northern Iraq are taking part in the operation to drive Islamic State from the city of Mosul, Turkish military sources have told Reuters.

Turkey has been locked in a row with Iraq's central government over the presence of Turkish troops at Bashiqa and over who should take part in the U.S.-backed assault on Mosul.

Peshmerga forces advance in the east of Mosul to attack Islamic State militants in MosulCredit:
AZAD LASHKARI

"Around half of the 3,000 are currently taking part in the operation. The other half are being kept in reserve," one of the sources told Reuters.

The source said there were Shi'ites, Yazidis and Christians in the force, which also included Turkmen fighters.

"There is currently no participation in the operation by the Turkish military, but developments are being watched very closely," the source said.

Dark clouds over Isil stronghold

Iraq's military and the country's Kurdish forces are on the move to the south and east of the Islamic State group-held city of Mosul.

The early Monday morning development follows Iraqi Prime Minister Haider al-Abadi's announcement that the long-awaited fight to retake Mosul has begun.

Convoys of Iraqi, Kurdish and U.S. forces could be seen moving east of Mosul into the early hours of Monday. Along the front line, U.S.-led coalition airstrikes sent plumes of smokes into the air and heavy artillery rounds could be heard.

Mosul, Iraq's second largest city, has been under IS rule for more than two years and still home to more than a million civilians according to estimates from the United Nations. The fight is expected to be the most complex yet for Iraq's military.

Very heavy gunfire now as Peshmerga meets ISIS in the town of Shakoli. Pesh expecting to reach #Mosul perimeter in three days. Ambitious